[bit.cast]

# 22 General utilities library [[utilities]](./#utilities)

## 22.11 Bit manipulation [[bit]](bit#cast)

### 22.11.3 Function template bit_cast [bit.cast]

[🔗](#lib:bit_cast)

`template<class To, class From>
  constexpr To bit_cast(const From& from) noexcept;
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L15691)

*Constraints*: 

- [(1.1)](#1.1)

sizeof(To) == sizeof(From) is true;

- [(1.2)](#1.2)

is_trivially_copyable_v<To> is true; and

- [(1.3)](#1.3)

is_trivially_copyable_v<From> is true[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L15699)

*Mandates*: Neither To nor From are consteval-only types ([[expr.const]](expr.const "7.7 Constant expressions"))[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L15703)

*Constant When*: To, From, and the types of all subobjects
of To and From are types T such that:

- [(3.1)](#3.1)

is_union_v<T> is false;

- [(3.2)](#3.2)

is_pointer_v<T> is false;

- [(3.3)](#3.3)

is_member_pointer_v<T> is false;

- [(3.4)](#3.4)

is_volatile_v<T> is false; and

- [(3.5)](#3.5)

T has no non-static data members of reference type[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L15715)

*Returns*: An object of type To[.](#4.sentence-1)

Implicitly creates objects nested within the result ([[intro.object]](intro.object "6.8.2 Object model"))[.](#4.sentence-2)

Each bit of the value representation of the result
is equal to the corresponding bit in the object representation
of from[.](#4.sentence-3)

Padding bits of the result are unspecified[.](#4.sentence-4)

For the result and each object created within it,
if there is no value of the object's type corresponding to the
value representation produced, the behavior is undefined[.](#4.sentence-5)

If there are multiple such values, which value is produced is unspecified[.](#4.sentence-6)

A bit in the value representation of the result is indeterminate if
it does not correspond to a bit in the value representation of from or
corresponds to a bit
for which the smallest enclosing object is not within its lifetime or
has an indeterminate value ([[basic.indet]](basic.indet "6.8.5 Indeterminate and erroneous values"))[.](#4.sentence-7)

A bit in the value representation of the result is erroneous
if it corresponds to a bit
for which the smallest enclosing object has an erroneous value[.](#4.sentence-8)

For each bit b in the value representation of the result
that is indeterminate or erroneous,
let u be the smallest object containing that bit enclosing b:

- [(4.1)](#4.1)

  If u is of unsigned ordinary character type or std​::​byte type,u has an indeterminate value
if any of the bits in its value representation are indeterminate, or
otherwise has an erroneous value[.](#4.1.sentence-1)

- [(4.2)](#4.2)

  Otherwise, if b is indeterminate, the behavior is undefined[.](#4.2.sentence-1)

- [(4.3)](#4.3)

  Otherwise, the behavior is erroneous, and the result is as specified above[.](#4.3.sentence-1)

The result does not otherwise contain any indeterminate or erroneous values[.](#4.sentence-10)